Electrostatic chuck with internal flow adjustments for improved temperature distribution

ABSTRACT

An electrostatic chuck is described with external flow adjustments for improved temperature distribution. In one example, an apparatus has a dielectric puck to electrostatically grip a silicon wafer. A cooling plate is fastened to and thermally coupled to the ceramic puck. A supply plenum receives coolant from an external source and a plurality of coolant chambers are thermally coupled to the cooling plate and receive coolant from the supply plenum. A return plenum is coupled to the cooling zones to exhaust coolant from the cooling zones. A plurality of adjustable orifices are positioned between the supply plenum and a respective one of the cooling zones to control the flow rate of coolant from the supply plenum to the cooling zones.

TECHNICAL FIELD

Embodiments of the present invention relate to the microelectronicsmanufacturing industry and more particularly to temperature controlledchucks for supporting a workpiece during plasma processing.

BACKGROUND

In the manufacture of semiconductor chips a silicon wafer or othersubstrate is exposed to a variety of different processes in differentprocessing chambers. The chambers may expose the wafer to plasmas,chemical vapors, metals, laser etching, and various deposition and acidetching processes in order to form circuitry and other structures on thewafer. During these processes, the silicon wafer may be held in place byan electrostatic chuck (ESC). The chuck holds the wafer by generating anelectrostatic field to clamp the back side of the wafer to a flatsurface or puck surface of the chuck.

As fabrication techniques for plasma processing equipment advance, suchas those designed to perform plasma etching of microelectronic devicesand the like, the temperature of the wafer during processing becomesmore important.

ESCs have been designed for thermal uniformity across the surface of thesubstrate, sometimes called a workpiece. ESCs use liquid cooling toabsorb the plasma power heat and remove it from the chuck. An ESC mayalso include independently controlled heaters in multiple zones. Thisallows for a wider process window under different process and plasmaconditions. Individual heater zones in the radial direction can createvarious radial temperature profiles which compensate for other etchprocess radial non-uniformities. However, radial heaters cannot affectnon-uniformities in the azimuthal direction.

In semi-conductor etch processing, the temperature of a wafer duringprocessing influences the rate at which structures on the wafer areetched. Other processes may also have a temperature dependence. Thistemperature influence is present, for example, in conductor etchapplications in which very precise wafer temperature control helps toobtain a uniform etch rate. A more precise thermal performance allowsfor more precisely formed structures on the wafer. Uniform etch ratesacross the wafer allow smaller structures to be formed on the wafer.Thermal performance or temperature control is therefore a factor inreducing the size of transistors and other structures on a silicon chip.

SUMMARY

An electrostatic chuck is described with internal flow adjustments forimproved temperature distribution. In one example, an apparatus has adielectric puck to electrostatically grip a silicon wafer. A coolingplate is fastened to and thermally coupled to the ceramic puck. A supplyplenum receives coolant from an external source and a plurality ofcoolant chambers are thermally coupled to the cooling plate and receivecoolant from the supply plenum. A return plenum is coupled to thecooling zones to exhaust coolant from the cooling zones. A plurality ofadjustable orifices are positioned between the supply plenum and arespective one of the cooling zones to control the flow rate of coolantfrom the supply plenum to the cooling zones.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention are illustrated by way of example,and not limitation, in the figures of the accompanying drawings inwhich:

FIG. 1 is a schematic of a plasma etch system including a chuck assemblyin accordance with an embodiment of the present invention;

FIG. 2 is a simplified cross-sectional diagram of a portion of anelectrostatic chuck in accordance with an embodiment of the invention;

FIG. 3 is a simplified cross-sectional diagram of a model of ESCtemperature and thermal conduction for an electrostatic chuck inaccordance with an embodiment of the invention;

FIG. 4 is a diagram of a top elevation contour line graph of thetemperature of a wafer in a processing chamber;

FIG. 5 is an isometric view of an electrostatic chuck in accordance withan embodiment of the invention;

FIG. 6 is an isometric view of the electrostatic chuck of FIG. 5 withthe puck removed in accordance with an embodiment of the invention;

FIG. 7 is an isometric view of an electrostatic chuck cut in halfaccordance with an embodiment of the invention;

FIG. 8 is a cross-sectional view of a feedthru channel of anelectrostatic chuck in accordance with an embodiment of the invention;

FIG. 9 is a cross-sectional cutaway view of a ceramic puck and a coolingplate in accordance with an embodiment of the invention;

FIG. 10 is a cross-sectional cutaway view of a ceramic puck and coolingplate showing connection screws in accordance with an embodiment of theinvention;

FIG. 11 is a cross-sectional cutaway view of a valve of an electrostaticchuck with arrows to indicate coolant flow in accordance with anembodiment of the invention;

FIG. 12 is a top isometric view of the middle plate of a coolant plateof an electrostatic chuck in accordance with an embodiment of theinvention;

FIG. 13 is a cross-sectional isometric view of an alternativeelectrostatic chuck in accordance with an embodiment of the invention;

FIG. 14A is a top isometric view of a mid plate over a bottom plate ofan electrostatic chuck in accordance with an embodiment of theinvention;

FIG. 14B is a top isometric view of a bottom plate of an electrostaticchuck in accordance with an embodiment of the invention;

FIG. 15A is a bottom isometric view of a bottom plate of anelectrostatic chuck in accordance with an embodiment of the invention;

FIG. 15B is a bottom isometric view of a cooling plate with the bottomplate of an electrostatic chuck removed in accordance with an embodimentof the invention;

FIG. 15C is a bottom isometric view of a top plate of an electrostaticchuck in accordance with an embodiment of the invention;

FIG. 16 is a cross-sectional side view of a cooling plate of anelectrostatic chuck in accordance with an embodiment of the invention;

FIG. 17 is a cross-sectional side view of a cooling plate of anelectrostatic chuck with a plastic insert attached proximate an orificeof the cooling plate in accordance with an embodiment of the invention;

FIG. 18 is a diagram of calibrating the orifice flow rates for a coolingplate of an electrostatic chuck in accordance with an embodiment of theinvention; and

FIG. 19 is a process flow diagram of adjusting flow rates in anelectrostatic chuck in accordance with an embodiment of the invention.

DETAILED DESCRIPTION

In the following description, numerous details are set forth, however,it will be apparent to one skilled in the art, that the presentinvention may be practiced without these specific details. In someinstances, well-known methods and devices are shown in block diagramform, rather than in detail, to avoid obscuring the present invention.Reference throughout this specification to “an embodiment” or “oneembodiment” means that a particular feature, structure, function, orcharacteristic described in connection with the embodiment is includedin at least one embodiment of the invention. Thus, the appearances ofthe phrase “in an embodiment” or “in one embodiment” in various placesthroughout this specification are not necessarily referring to the sameembodiment of the invention. Furthermore, the particular features,structures, functions, or characteristics may be combined in anysuitable manner in one or more embodiments. For example, a firstembodiment may be combined with a second embodiment anywhere theparticular features, structures, functions, or characteristicsassociated with the two embodiments are not mutually exclusive.

As used in the description of the invention and the appended claims, thesingular forms “a”, “an” and “the” are intended to include the pluralforms as well, unless the context clearly indicates otherwise. It willalso be understood that the term “and/or” as used herein refers to andencompasses any and all possible combinations of one or more of theassociated listed items.

The terms “coupled” and “connected,” along with their derivatives, maybe used herein to describe functional or structural relationshipsbetween components. It should be understood that these terms are notintended as synonyms for each other. Rather, in particular embodiments,“connected” may be used to indicate that two or more elements are indirect physical, optical, or electrical contact with each other.“Coupled” my be used to indicate that two or more elements are in eitherdirect or indirect (with other intervening elements between them)physical, optical, or electrical contact with each other, and/or thatthe two or more elements co-operate or interact with each other (e.g.,as in a cause an effect relationship).

The terms “over,” “under,” “between,” and “on” as used herein refer to arelative position of one component or material layer with respect toother components or layers where such physical relationships arenoteworthy. For example in the context of material layers, one layerdisposed over or under another layer may be directly in contact with theother layer or may have one or more intervening layers. Moreover, onelayer disposed between two layers may be directly in contact with thetwo layers or may have one or more intervening layers. In contrast, afirst layer “on” a second layer is in direct contact with that secondlayer. Similar distinctions are to be made in the context of componentassemblies.

The temperature uniformity across the surface of an ESC has beenimproved with improved cooling plate and heater designs and improvementsin bonding the cooling plate to the puck that holds the workpiece.However, these designs and processes are still subject to manufacturingvariations, which can lead to significant thermal non-uniformity. Forsome implementations, a spatial temperature variation of less than+/−0.3° C. across the wafer is desired.

The temperature of the ESC can be more precisely controlled by using aplurality of small heaters, but this requires complex wiring and controlsystems, at significant cost. In embodiments described herein, a plasmaprocessing chuck includes a plurality of orifices that can beindependently drilled, expanded, exchanged to different sizes. Theorifices control the flow of coolant to different areas of the coolingbase. The thermal performance of the chuck can be improved through theadjustment of many small flow restrictors in the cooling plate. Thelocal values of R, the thermal resistance of the cooling plate, can alsobe changed for the cooling plate. This possibility has not existed inprevious ESC designs. As described herein, this new cooling plate issimple and can be calibrated, manufactured and used at low cost. Theadjustable orifices can be used to correct manufacturing variations, tocompensate for chamber and process inconsistencies, and to vary thetemperature for different areas of the workpiece.

FIG. 1 is a schematic of a plasma etch system 100 including a chuckassembly 142 in accordance with an embodiment of the present invention.The plasma etch system 100 may be any type of high performance etchchamber known in the art, such as, but not limited to, Enabler™, DPS II,AdvantEdge™ G3, E-MAX®, Axiom, Orion, or Mesa CIP chambers, all of whichare manufactured by Applied Materials of California, USA. Othercommercially available etch chambers may similarly utilize the chuckassemblies described herein. While the exemplary embodiments aredescribed in the context of the plasma etch system 100, the chuckassembly described herein is also adaptable to other processing systemsused to perform any plasma fabrication process (e.g., plasma depositionsystems, etc.)

Referring to FIG. 1, the plasma etch system 100 includes a groundedchamber 105. Process gases are supplied from gas source(s) 129 connectedto the chamber through a mass flow controller 149 to the interior of thechamber 105. Chamber 105 is evacuated via an exhaust valve 151 connectedto a high capacity vacuum pump stack 155. When plasma power is appliedto the chamber 105, a plasma is formed in a processing region over aworkpiece 110. A plasma bias power 125 is coupled into a chuck assembly142 to energize the plasma. The plasma bias power 125 typically has alow frequency between about 2 MHz to 60 MHz, and may be, for example, inthe 13.56 MHz band. In an example embodiment, the plasma etch system 100includes a second plasma bias power 126 operating at about the 2 MHzband which is connected to an RF match 127. The plasma bias power 125 isalso coupled to the RF match and also coupled to a lower electrode 120via a power conduit 128. A plasma source power 130 is coupled throughanother match (not shown) to a plasma generating element 135 to providehigh frequency source power to inductively or capacitively energize theplasma. The plasma source power 130 may have a higher frequency than theplasma bias power 125, such as between 100 and 180 MHz, and may, forexample, be in the 162 MHz band.

A workpiece 110 is loaded through an opening 115 and clamped to a chuckassembly 142 inside the chamber. The workpiece 110, such as asemiconductor wafer, may be any wafer, substrate, or other materialemployed in the semi-conductor processing art and the present inventionis not limited in this respect. The workpiece 110 is disposed on a topsurface of a dielectric layer 143 or puck of the chuck assembly that isdisposed over a cooling base assembly 144 of the chuck assembly. A clampelectrode (not shown) is embedded in the dielectric layer 143. Inparticular embodiments, the chuck assembly 142 may include differentheater zones, such as a center zone 141 and edge zones 199, each zone141, 199 may be independently controllable to the same or to differenttemperature set points.

A system controller 170 is coupled to a variety of different systems tocontrol a fabrication process in the chamber. The controller 170 mayinclude a temperature controller 175 to execute temperature controlalgorithms (e.g., temperature feedback control) and may be eithersoftware or hardware or a combination of both software and hardware. Thesystem controller 170 also includes a central processing unit 172,memory 173 and input/output interface 174. The temperature controller175 is to output control signals affecting the rate of heat transferbetween the chuck assembly 142 and a heat source and/or heat sinkexternal to the plasma chamber 105 for the various heater zones 141,199.

In embodiments, in addition to the different heaters, there may bedifferent coolant temperature zones. The coolant zones may includeseparate, independently controlled heat transfer fluid loops withseparate flow control that is controlled based on a zone-specifictemperature feedback loop. In the example embodiment, the temperaturecontroller 175 is coupled to a first heat exchanger (HTX)/chiller 177and may further be coupled to a second HTX/chiller 178 and a thirdHTX/chiller 179. The flow rate of the heat transfer fluid or coolantthrough conduits in the chuck assembly 142 may also be controlled by theheat exchangers.

One or more valves 185, 186 (or other flow control devices) between theheat exchanger/chillers 177, 178, 179 and fluid conduits in the chuckassembly 142 may be controlled by the temperature controller 175 toindependently control a rate of flow of the heat transfer fluid to eachof the different cooling zones. The heat transfer fluid may be a liquid,such as, but not limited to deionized water/ethylene glycol, afluorinated coolant such as Fluorinert® from 3M or Galden® from SolvaySolexis, Inc. or any other suitable dielectric fluids such as thosecontaining perfluorinated inert polyethers. While the presentdescription describes the ESC in the context of a plasma processingchamber, the ESC described herein may be used in a variety of differentchambers and for a variety of different processes.

FIG. 2 is a simplified cross-sectional diagram of a portion of anelectrostatic chuck (ESC) 200. There are at least four components forregulating the temperature of the chuck surface and therefore thetemperature of a wafer (not shown) on the chuck. A cooling plate 201,typically made from a thermally conducting metal serves as a heat sink.The cooling plate is bonded to a dielectric puck 202 with a hightemperature adhesive 204, such as silicone. The puck is typicallyceramic but may alternatively be made with other materials. Electrodes(not shown) are embedded within the puck to generate an electrostaticfield with which to grip a workpiece, such as a silicon substrate.Resistive heater traces 203 are also embedded within the puck fortemperature control.

The cooling plate 201 also includes channels 205 for coolant. Coolant ispumped through the channels to absorb heat from the cooling plate andpumped to a heat exchanger to cool the fluid which is then recirculatedback to the cooling plate. The cooling plate absorbs heat from theembedded heaters and the workpiece through the ceramic plate. Thetemperature uniformity depends on the quality of the ceramic puck 202,the elastomer bond 204, and the cooling plate channels 205. It alsodepends on how well heat is transferred from the workpiece to theceramic puck. All of these factors are subject to variations inmanufacture and use.

FIG. 3 is a simplified one-dimensional diagram of a model of ESCtemperature and thermal conduction. The diagram is presented using thesame components and reference numbers as in FIG. 2, however, only aportion of the FIG. 2 diagram is shown for reference. In this model, theceramic temperature, Tceramic, at a given location 220 is determined inpart by the “thermal resistances” of the cooling plate (R cooling plate)222 and the bond (R bond) 221. Heat is provided by the heater power (Qheater) 223 and removed by the cooling plate (T cooling plate 224) andby the coolant (T coolant 226). The thermal resistance is presented forpurposes of explanation. The components of FIG. 3 may be described asfollows:

Q heater 223: The heater power at a given point on the ESC surface isdetermined by the number of heater traces in the area, and theelectrical resistance of those heater traces. When the chuck is in use,heat is also applied by the plasma. For testing purposes, the heatersmay be used to simulate plasma processing or any other high temperatureprocessing or a different external or internal heat source may be used.If the heater traces produce sufficient heating, then the heater tracesmay be used. Rather than generating temperatures similar to those usedfor plasma processing, the heater traces may be used simply to generatea measureable heat flow from the ceramic puck 202 to the othercomponents.

R bond 221: The resistance of the bond is determined by the thermalconductivity of the bond material, the bond thickness, and the qualityof the bond connection both to the cooling plate and to the ceramicpuck.

T cooling plate 224: The temperature of the cooling plate is largelycontrolled by the conduction of heat from the ceramic puck through thebond and into the coolant. The flow of heat into the coolant at any onelocation 224 of the cooling plate is affected by at least twofactors: 1) the coolant temperature increases as it travels through thecooling plate so that the coolant at different locations of the coolingplate will be at different temperatures and 2) feedthrus and otherfeatures of the cooling plate constrain where the cooling channels canbe placed in the cooling plate so that some locations have more coolantflow then others.

R cooling plate 222: The thermal resistance of the cooling plate is acombined function of the local fluid heat transfer coefficient, thegeometry of the cooling plate, and the thermal conductivity of thecooling plate.

T coolant 226: The temperature of the coolant entering the cooling platemay be carefully controlled by a heat exchanger or chiller. However, asthe coolant travels through the cooling plate, its temperatureincreases. In a typical application, the coolant temperature may rise byup to 10° C. So the local coolant temperature at a given point on theESC varies greatly.

T ceramic: The temperature of the ESC ceramic at any one particularlocation 220 may be estimated using the relationship:

T ceramic=Q heater R bond+Q heater R cooling plate+T coolant.

This shows that to achieve a uniform temperature across the ceramicpuck, R cooling plate may be adjusted at each location to compensate forvariation of R bond, Q heater, and T coolant. Alternatively, another wayto achieve the most uniform ceramic temperature possible is to designthe heater traces (and hence Q heater) to compensate for the spatialvariations of the cooling plate temperature. In other words Q heater isadjusted based on variations in R cooling plate and T coolant.

In an ideal ESC design, the heater watt density will be matched toperfectly compensate for variations in the cooling plate temperature.The bond thickness is uniform. As a result, the ceramic temperature isuniform in every dimension. In any real manufactured ESC, the ceramictemperature is non-uniform due to several factors. First, the design ofthe heater traces may not be perfect. As a result an ideally uniformwatt density is difficult to achieve. Second, the heater traces aremanufactured or created using a screen printing process. Printing errorcauses the actual watt density to deviate still further from theimperfect values that were designed for the traces. Third, the bondthickness of the adhesive varies. As a result, a typical manufacturedESC does not have perfectly uniform bond heat resistance.

FIG. 4 is a diagram of a top elevation graph 400 of the temperature of awafer 404 on an ESC. This graph shows surface temperature as a functionof position on the wafer using contour lines 402. Such a diagram may begenerated based on a measurement of an actual ESC as it is heated by theconductive traces and cooled by coolant flowing through the channels ofthe cooling base. Such measurements may be made by heating a wafer andthen measuring the temperature at different positions using an infraredcamera. As shown, the temperature values shown on the surfacetemperature contour lines vary in a pattern that is related tomanufacturing and design features of the ESC. Contour lines are shownonly for integer temperature values in order to simplify the diagram.For an actual measurement, much higher accuracy, for example tenths of adegree may be desired.

In order to even out the temperatures and obtain a more uniformtemperature across the ESC, external adjustments can be made to thecoolant flow within the ESC. In one example, the cooling plate containsmany (e.g. 50+) small flow adjustable orifices. These orifices may beadjusted by mechanically changing their size or by replacing an insert,such as a sleeved tube. Adjustments to the coolant flow through theorifices may be based on a one-time calibration using an infra-redcamera. The calibration can compensate for manufacturing defects in theESC and drastically improve the thermal performance characteristics ofthe cooling plate. The calibration process may use the measurements toadjust each orifice based on feedback from an infra-red camera. Thecooling plate may be measured and the orifices adjusted in an iterativeprocess until the desired heat distribution is obtained.

FIG. 5 is an isometric view of an ESC 500 showing a ceramic puck 502over a cooling plate 504. The diagram is simplified and does not includeelectrical, coolant and control connections. The diagram also does notshow a variety of different “feedthru” holes in the ceramic puck. Theseholes are required to accommodate gas outlets, temperature probes, andwafer lift pins.

FIG. 6 is an isometric view of the ESC of FIG. 5 with the ceramic puckremoved so that only the cooling plate 504 is visible. The ceramic puckmay be attached to the cooling plate in any of a variety of differentways. Typically, the ceramic puck is attached with a bond, such asmetallic, nano-foil or silicone adhesive filled with a thermallyconductive material, such as alumina, although the invention is not solimited. The cooling plate includes feedthru holes 508 as mentionedabove. The periphery of the cooling plate includes mounting holes 507 toattach the ESC to a mounting carriage as shown in FIG. 1.

FIG. 7 is an isometric view of the same ESC 500 cut vertically in halfto show a cross section of the internal configuration. The cooling plate504, in this example is formed of three parts, a top plate 512 to whichthe ceramic puck is attached, a middle plate 514, and a bottom plate516. In the illustrated example, the top plate is also attached to thecarrier structure through peripheral bolt holes 507 and the top platesurrounds and protects the middle and bottom plates, however, theinvention is not so limited. The top plate may be constructed of adurable material able to survive a processing chamber environment, suchas ceramic or metal. The bottom plate is subject to less exposure to thechamber and so may be constructed of the same or a less durablematerial. The middle plate is protected by the top and bottom plates andmay be constructed of a different material, such as a plastic.

One of the feedthru holes 508 is visible in this cross-section. Itextends through top, middle, and bottom plates so that electricalconnectors, gases, or any other desired materials may be connectedthrough the cooling plate. Additional feedthrus (not shown) may extendonly partially through the cooling plate for other purposes.

FIG. 8 shows a feedthru in more detail. The feedthru may be provided bya sleeve 518 attached to the top 512 and bottom 516 plates by anadhesive or by welding 520, 522. In the illustrated example, the sleeveis sealed against the middle plate using O-rings 524. This allows a sealto be made against a plastic material for which welding is not possible.The connections may be made in any of a variety of other ways dependingon the materials used for the sleeve and the plates, including bybrazing or using adhesives, or epoxy, among others. The sleeve protectsthe electrical or other components (not shown) inside the sleeve. Thesleeve also provides additional rigidity to the cooling plate.

FIG. 9 is a cross-sectional cutaway view of the ceramic puck 502 bondedto the cooling plate 504. Electrical connectors and feedthrus are notshown, however, the upper portion 512, middle portion 514 and lowerportion 516 are shown. Cooling chambers 530 are defined as spacesbetween the middle 514 and upper 512 portions. A supply plenum 532 isdefined between the middle 514 and bottom 516 portions. The feedthrus(not shown) pass through the cooling chambers and can interfere with theflow of coolant and the design of the coolant chambers.

In this example, the orifices are in channels between the supply plenumand each coolant chamber. The size of each orifice controls the flow ofcoolant from the supply plenum to its associated coolant chamber. Thechannels are from the bottom of the middle plate where there is aninlet, through the middle plate to the top of the middle plate wherethere is an outlet. By changing the size of the orifice, the flowthrough each individual cooling zone can be changed. The flow can beadjusted independently for each orifice to compensate for differentplasma conditions or non-uniformities.

FIG. 10 is a cross-sectional side view as in FIG. 9 showing the boltedconstruction of the cooling plate. The bottom plate 516 is fastened tothe top plate 512 using a series of screws 537. The screws are driveninto threaded holes 538 in the top plate. The mid plate 514 issandwiched between the top and bottom plates. In the illustratedexample, the top plate includes an O-ring 540 around its periphery toseal against the bottom plate and keep coolant inside the supply andreturn plenums. The mid plate also has an O-ring 542 around itsperiphery to seal the supply plenum against the bottom plate.

The screw-in construction with O-rings allows the cooling plate toeasily be disassembled and reassembled. After disassembly, the orifices536 may easily be accessed for adjustment. The size of the opening ofeach orifice may be adjusted by machining, drilling, or changinginserts. In addition, some of the orifices may be closed or blocked toprevent coolant flow into certain areas. The cooling plate may then bereassembled and tested for heat distribution or reassembled for use inproduction. The specific mechanical construction of the cooling platemay be modified to adapt to different implementations.

FIG. 11 shows the flow of coolant fluid from inlet to outlet in across-sectional diagram of a portion of the cooling plate. Coolantenters the cooling plate through one or more coolant supply ports 562.The supply ports provide the coolant to one or more supply plenums 532between the bottom plate 516 and the middle plate 514. The supply plenumis open to one side of the orifices 536 in the lower plate 516. Coolantflows through the orifices 536, through the middle plate 514 intorespective cooling chambers 530 between the middle plate 514 and theupper plate 512. From the cooling chambers, the coolant flows to one ormore return channels 566 and then to one or more return ports 564. Thereturn ports conduct the coolant to one or more heat exchangers as shownin FIG. 1 to be cooled and recycled back to the supply ports.

FIG. 12 is a top isometric view of the middle plate 514 of the coolantplate showing features that may be cast, stamped, or machined into themiddle plate. The middle plate is attached to the bottom plate 516 asshown. The middle plate has hexagonal areas 570 that define the coolantchambers 530 with respect to the top plate (not shown). Each hexagonalarea is supplied by the outlet channel 568 from an orifice. The coolantfills the space between the hexagonal area 570 and the top plate,cooling the top plate in the hexagonal area. The coolant then flows intoreturn channels 566 that surround each hexagonal area. The returnchannels lead to a broader circular channel that surrounds all of thehexagonal areas of the middle plate and follows a path near theperiphery of the plate. From the circular channel, the coolant flowsinto radial channels that lead radially outward away from the circularchannel and the hexagonal areas to return outlets 564. The returnoutlets are on the outer edge of the middle plate as shown but may beplaced in a different location, depending on the particularimplementation.

The hexagonal areas are each supplied by a different orifice which maybe supplying coolant at a different flow rate from other orifices. Byfeeding the supplied coolant into common channels and a common returnplenum as defined by the common channels 566, the fluid pressure througheach of the orifices may be equalized. The return ports all contributeequally to drawing the coolant away from the cooling plate.

While hexagonal areas are shown, the invention is not so limited. Thehexagonal shape provides for a large capacity and length of sharedcoolant return channels for the amount of cooling area. The coolantchambers may be arranged in rectangular configurations to provide forstraight coolant return channels. This may improve flow. An alternatingbrick style configuration may be used or any of a variety of polygonaland curved coolant areas may be used, depending on the particularimplementation.

The overall cooling operation can be summarized as follows. The parts ofthe cooling plate define a supply plenum that receives coolant throughsupply ports and distributes the coolant supply across the coolantplate. The supply plenum in this example is defined between the bottomplate and the mid plate. However, the supply plenum may instead bedefined by the mid plate and the top plate.

From the supply plenum, coolant flows through adjustable orifices intocooling zones between the top plate and mid plate. The cooling zones maybe in a different location, depending on the particular implementation.

From the cooling zones, flow proceeds into larger spaces between the topplate and the mid plate. These larger spaces form a return plenum.Coolant leaves the ESC from the return plenum through return portsthrough the mid and bottom plate.

FIG. 13 shows an alternative cooling plate suitable for use with an ESCas described above. The cooling plate 700 is shown with the ceramic puckand other parts removed. This isometric cross-sectional diagram is alsosimplified and does not show electrical and coolant connections. O-ringgrooves and other features are also omitted.

The cooling plate 700 is an assembly of three plates, a top plate 702, amid plate 704, and a bottom plate 706. As in the example of FIG. 7, thethree plates may be joined together with screws, welding, brazing,adhesives or some combination of these approaches and techniques. Inthis example, a large number of orifices 724 are embedded in the middlecooling plate. By adjusting the size of each orifice, the flow througheach individual cooling zone can be adjusted.

As in the example of FIG. 7, a ceramic puck (not shown) is bonded to thecooling plate 700. Electrical connectors allow the ceramic puck to beenergized at clamp electrodes to grip a workpiece. A variety offeedthrus 714 provide other connections to the ceramic puck.

The cooling chambers 718 are defined by these two portions and arebetween these two portions. In this example, the volumes of the coolingchambers formed are in the top plate, rather than in the mid plate. Asupply plenum 720 between the mid plate 704 and the bottom plate 706supplies coolant at the base of the orifices to flow through theorifices.

FIG. 14A is a top isometric view of the mid plate 704 over the bottomplate 706. The mid plate has feedthrus 714 as mentioned above and aseries of general return ports 708 which collect coolant from theindividual cooling chambers and feed it back to return lines. The midplate 704 also has an arrangement of multiple lands that define thecooling chambers with respect to the top plate (not shown). The landseach include the orifice 724 through which coolant is allowed to enterthe cooling chamber.

FIG. 14B is a top isometric view of the bottom plate 706. The bottomplate includes the feedthrus 714 and the return ports 708 which are alsoformed in the mid plate. This view also shows the screws 716that holdthe bottom plate to the top plate to hold the cooling plate together.

The bottom plate is also fitted with one or more supply ports 730. Inthe illustrated example there are six supply ports, however there may befewer or many more, depending on the particular implementation. Thesupply ports provide coolant into the area between the top surface 728of the bottom plate and the bottom surface of the mid plate. This areaserves as the supply plenum 720 for the orifices 724 in the mid plate.Coolant provided into the supply ports will be contained in part by thetop surface 728 of the bottom plate 706. Pressure from the supply portswill then drive the coolant into the orifices 724 of the mid plate.

FIG. 15A is a bottom isometric view of the bottom plate 706 of FIG. 14B.The bottom side of the bottom plate includes feedthrus 714 and returnports 708. The supply ports 730 allow coolant to be supplied through thebottom plate toward the opposite side of the bottom plate into thesupply plenum. The supply ports have attachment points to allow acoolant supply and heat exchanger system to be coupled to the supplyports. The bottom plate also has holes 708 for the return ports tosupply coolant back to the heat exchanger system after it has passedthrough the coolant chambers to cool the cooling plate and the chuck'stop surface.

FIG. 15B is a bottom isometric view of the cooling plate 700 with thebottom plate removed so that the mid plate is exposed. From the bottomside, the orifices 724 are visible as are the feedthrus 714 and returnports 708. The bottom surface of the mid plate 704 forms an uppersurface of the supply plenum 720 so that coolant supplied into the areabelow the bottom of the mid plate will be captured between the bottomsurface of the mid plate and a top surface 728 of the bottom plate. Thecoolant may flow freely from the supply plenum into the orifices. Thecoolant that flows past the orifices will enter into the respectivecoolant chamber for orifice.

FIG. 15C is a bottom isometric view of the top plate 706. In addition tofeedthrus 714 and threaded holes 738, an outline for each coolantchamber 718 is shown. The individual chambers are aligned over eachrespective orifice 724 so that coolant fluid that passes through eachvalve is delivered into a respective coolant chamber.

The cooling zones are shown as circular and uniformly sized. The shape,size, and positions of the cooling zones may be modified to suit anyparticular local cooling requirements. In addition, the height of thechannel in the cooling zone (between the top and mid plate) may bemodified to achieve a uniform, or a non-uniform, heat transfer acrossthe zone.

FIG. 16 is a cross-sectional side view of the cooling plate with allthree of the plates 702, 704, 706 installed together. Coolant in thesupply plenum 720 between the bottom 706 and mid 704 plates flowsthrough the orifice 724 into a cooling chamber 718 above the valve. Thecoolant will absorb heat from the top plate 702 in the cooling chamberand then move to the return plenum 734. The cooling chamber and thereturn plenum are defined within a space between the top 702 and mid 704plates and defined by the shape and the configuration of the two plateswith respect to each other. From the return plenum, the coolant flowsthrough return ports to heat exchangers to be cooled and then returnedback to the supply plenum 720 through supply ports.

FIG. 17 shows a similar cross-sectional view of the cooling plate as inFIG. 16 with the three plates attached together. While each orifice 724can be modified by machining, the size of the orifice may also bemodified using interchangeable parts. A plastic insert 726 may be placedbetween the supply plenum 712 and the orifice 724 or between the orificeand the coolant chamber 718 to restrict the flow rate through theorifice. The plastic insert may have an exterior adapted to stay inplace in the middle plate and an interior sleeve with a diameterdesigned to restrict flow. Different inserts may be provided withdifferent diameter sleeves to allow for different flow adjustments. Theplastic insert allows the flow rate through each orifice to be adjustedindividually.

FIG. 18 is a diagram of determining appropriate coolant flow orificesize adjustments for a cooling plate 700. In the illustrated example, aceramic puck 702 is attached to a cooling plate 700. The ceramic plateis heated externally or using its own heaters. Heat exchangers (notshown) are attached to the supply and return ports of the ESC through anadapter plate 754. As the ESC is heated and cooled, the temperature ofthe ceramic plate is measured using, for example, an infrared camera 746or a temperature monitor wafer.

The camera is coupled to a calibration system 748 that is controlled bya calibration system controller or processor 752 to measure temperaturebased on the camera image or to determine orifice adjustments. Thecalibration system 748 may be a computer or a dedicated system designedfor this purpose. The infrared image from the camera is analyzed in animage analysis module 750 and compared to a reference or intendedinfrared image. Differences between the measured temperature at eachpoint on the ceramic plate and the desired temperature for that pointare then used by the controller to determine orifice adjustments for thevarious cooling zones across the ceramic plate. The cooling plate may bedisassembled, the flow rates adjusted, and the cooling platereassembled. The adjusted cooling plate may then be used directly forfabrication, it may also be retested. Any resulting temperaturedifferences are observed by the IR camera or a temperature monitorwafer. Further adjustments may then be made until the desired coolantflow is obtained.

The flow to each cooling zone may be set during a one-time calibrationprocess. This calibration process may be used to compensate formanufacturing non-uniformities. The cooling plate may also be removedfrom production and recalibrated to adjust for changes over time or foruse in a different chamber or process. If the orifices have beenmachined to be larger, they cannot be machined to made smaller, howeverinserts or sleeves may be used to reduce coolant flow as desired for aparticular cooling plate.

The calibration process may be described as shown in FIG. 19. First at802, the assembled ESC is placed in a test fixture. The test fixture hasthe IR camera 746 and an adapter plate 754 which makes coolant 756 andelectrical 758 connections to the ESC.

At 804, heat is applied to the ESC. This may be done in a processchamber or oven, or by activating or energizing heater traces within theESC. At 806, the temperature of the top plate of the ESC measured. Inthe system of FIG. 18, the dielectric puck is imaged by an infraredcamera, but the invention is not so limited.

At 808, a computer-based control algorithm may be used to analyze thetemperatures of the ESC and at 810 to determine adjustments. At 812, theflow rate through each orifice may be adjusted serially orsimultaneously by disassembling the cooling plate. The IR camera maythen image the puck again to determine if any further adjustments shouldbe made. This adjustment process may continue until the desiredtemperature profile (uniform or otherwise) is achieved.

The individual adjustment of each orifice may be used to achieveextremely uniform wafer temperature during a fabrication process.Changes in coolant flow may be used to compensate for variations in thethickness of the bond between the ceramic puck and the cooling plate andfor variations in the printing of heater traces within the ceramic puck.In addition the ESC may be calibrated to a deliberately non-uniformtemperature profile. This may be used to compensate for chamber levelasymmetries.

It is to be understood that the above description is intended to beillustrative, and not restrictive. For example, while flow diagrams inthe figures show a particular order of operations performed by certainembodiments of the invention, it should be understood that such order isnot required (e.g., alternative embodiments may perform the operationsin a different order, combine certain operations, overlap certainoperations, etc.). Furthermore, many other embodiments will be apparentto those of skill in the art upon reading and understanding the abovedescription. Although the present invention has been described withreference to specific exemplary embodiments, it will be recognized thatthe invention is not limited to the embodiments described, but can bepracticed with modification and alteration within the spirit and scopeof the appended claims. The scope of the invention should, therefore, bedetermined with reference to the appended claims, along with the fullscope of equivalents to which such claims are entitled.

What is claimed is:
 1. An apparatus comprising: a dielectric puck toelectrostatically grip a silicon wafer; a cooling plate fastened to andthermally coupled to the ceramic puck; a supply plenum to receivecoolant from an external source; a plurality of coolant chambersthermally coupled to the cooling plate, the coolant chambers to receivecoolant from the supply plenum; a return plenum coupled to the coolingzones to exhaust coolant from the cooling zones; and a plurality ofadjustable orifices between the supply plenum and a respective one ofthe cooling zones to control the flow rate of coolant from the supplyplenum to the cooling zones.
 2. The apparatus of claim 1, furthercomprising a plurality of return ports to return coolant from thecooling zones for resupply to the supply plenum.
 3. The apparatus ofclaim 1, wherein the adjustable orifices each comprise: an orificebetween the supply plenum and a respective cooling zone; and aninterchangeable insert to control coolant flow through the orifice. 4.The apparatus of claim 1, wherein the cooling plate comprises a middleplate and wherein the adjustable orifices are formed in the middleplate.
 5. The apparatus of claim 4, wherein the cooling plate furthercomprises a top plate and the bottom plate, wherein the middle plate issandwiched between the top plate and the bottom plate, wherein thecooling plate is disassembled to access the middle plate.
 6. Theapparatus of claim 5, wherein the orifices of the middle plate aremachined to adjust the flow rate when the cooling plate is disassembled.7. The apparatus of claim 5, further comprising a plurality of insertsto restrict flow through a respective orifice, the inserts beingexchangeable to provide different flow rates.
 8. An apparatuscomprising: a dielectric puck to electrostatically grip a silicon wafer;a top plate of a cooling plate, the top plate being fastened to theceramic puck; a middle plate of a cooling plate the middle plate havinga plurality of adjustable orifices and defining a plurality of coolantchambers between the middle plate and the top plate, the coolantchambers each being in communication with at least one orifice to allowcoolant to flow through the middle plate to a respective coolantchamber; a bottom plate of a cooling plate, the bottom plate defining asupply plenum between the bottom plate and the middle plate to supplycoolant to the orifices; and wherein the flow rate through each orificeis independently adjustable to control coolant flow through eachrespective one of the orifices.
 9. The apparatus of claim 8, wherein theorifices comprise openings in the middle plate, wherein the middle platemay be dissembled from the top plate and the bottom plate to machine theorifices to adjust the flow rate through each respective orifice, andwherein the middle plate may be assembled to the top plate and thebottom plate for use after the machining.
 10. The apparatus of claim 8,wherein the middle plate defines return plenums to conduct coolant fromthe coolant chambers to a return port.
 11. The apparatus of claim 10,wherein the middle plate has hexagonal areas to define the coolantchambers and coolant channels of the return plenums surrounding eachhexagonal area.
 12. The apparatus of claim 11, the middle plate furthercomprising a circular channel surrounding the hexagonal areas andwherein the coolant channels conduct the coolant into the circularchannel of the middle plate.
 13. The apparatus of claim 11, wherein eachhexagonal area is supplied by a different one of the plurality oforifices.
 14. A method for adjusting coolant flow in an electrostaticchuck, the method comprising: heating a dielectric puck, the dielectricpuck being for electrostatically gripping a silicon wafer; detectingheat at a plurality of locations on a top surface of the dielectricpuck, the locations each being thermally coupled to at least one of aplurality of coolant chambers of the electrostatic chuck; and adjustinga plurality of orifices to control coolant flow into the coolantchambers based on the detected heat.
 15. The method of claim 14, whereindetecting heat comprises imaging the dielectric puck during flowingcoolant into the coolant chambers through the orifices and duringapplying heat to the dielectric puck.
 16. The method of claim 15,wherein applying heat comprises activating heaters within theelectrostatic chuck.
 17. The method of claim 14 wherein adjusting aplurality of orifices comprises independently changing the flow ratethrough each of the plurality of orifices to control the flow of coolantfrom a supply plenum to a respective coolant chamber.
 18. The method ofclaim 14, wherein detecting heat comprises determining a temperaturelevel at different areas of the dielectric puck, the different areascorresponding to different coolant chambers.
 19. The method of claim 18,wherein adjusting the orifices comprises increasing coolant flow tocoolant chambers corresponding to hotter areas and decreasing coolantflow to coolant chambers corresponding to cooler areas.
 20. The methodof claim 14, wherein adjusting orifices comprises disassembling theelectrostatic chuck, machining at least a subset of the plurality of theorifices to change the respective flow rate, and reassembling theelectrostatic chuck.